The Role of the Corticostriatal System in Specific Language Impairment (SLI) Although the acquisition of language is nearly universal among humans, some are less adept than others. Poor acquisition of language is a common feature of many neuropsychiatric disorders; however, poor language development can occur in individuals who have no obvious causes as found in specific language impairment (SLI). SLI is a common neurodevelopmental disorder occurring in approximately 7 to 8% of school-age children that persists well into adulthood. The etiology of SLI is unknown; however, based on emerging behavioral evidence, the corticostriatal system that supports procedural and reinforcement learning may account for, at least in part, language learning difficulties in SLI. At this time, thre is little brain imaging data looking at the role of the corticostriatal system, subcortical structues in particular, in SLI. Thus, we have asked whether there is neuroanatomical and neurofunctional evidence showing that the corticostriatal system important to cognitive learning also contributes to individual differences in language. To address this question, the proposed project will follow up the findings from a recent pilot structural imaging study (SLI=12, Control=12) using anatomical magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) to examine the macrostructure and the microstructure of the basal ganglia and the thalamus, which are the primary subcortical components of the corticostriatal system. The pilot results provided strong evidence (effect sizes > 0.8) of differences in the relative volume and fractional anisotropy (FA) of the regions of interest between groups. In this proposed project, we will first expand on the pilot findings by increasing the sample size up to 35 participants per group (SLI, control), and extend the age range to adolescents, given that adolescence is a time of profound brain change. Then, we will compare structural and functional connectivity in the corticostriatal loops between adolescents with and without SLI by using diffusion tensor tractography and resting-state functional MRI. Last, we will examine the brain-behavior relationship in individuals with SLI to enhance the translation of brain findings to clinical applications. We hypothesize that individuals with SLI will show macrostructural and microstructural abnormality in the basal ganglia (in particular the putamen and the nucleus accumbens based on our pilot findings) and the thalamus. In addition, individuals with SLI will show altered white matter organization of the corticostriatal loops as well as abnormal functional synchrony of the basal ganglia with the cortical regions. We also hypothesize that individuals with SLI will have poor performance on cognitive tasks that have been well established to involve the corticostriatal loops, and the brain measures will predict language status and cognitive learning performance. Completion of the aims will bring insights into the role of the corticostriatal system in SLI. The proposed project wll have a positive impact on the neural mechanisms underlying individual differences in language acquisition. 1